Plain steel fasteners on Roadster bottom pans = Galvanic Corrosion

[ShawnA]

I was under the Roadster yesterday to program the rear antenna of the TPMS system.
I had to remove the pan under the two blowers. My Roadster still has 2 motors on the fans.

I was disappointed to see so many rusted fasteners on the undercarriage holding the various aluminum panels
in place.
Both the fasteners and the fender washers were badly rusted.
I replaced the 4 plain steel bolts and washers with stainless steel.
The screws were M6 x 1mm x 16 mm long.
I was able to get a 5 pack of M6 x 1mm x 20 mm long and some stainless fender washers 1/4" hole x 1" OD
at Lowes. The extra length did not cause any problems here.

This worked well for the 4 screws that I removed and replaced.
There are many more rusted fasteners.
I have a box of M6 x 1mm x 16 mm long screws coming from McMaster.
I will replace all of the plain steel screws and fender washers while I still can...

There were additional fasteners on the pan that I believe were M4 with washers.
Both the M4 size fasteners and their washers were stainless steel.

My Roadster is not a high mileage car but it is exposed to rain and minerals from the roads here in the Midwest.

I am spreading the word after reading of the galvanic corrosion on the Ecohitch and the power steering failures
on the Model S related to galvanic corrosion...
Unfortunately, we have it on the Roadster with the steel screws and washers in contact with the aluminum bottom pans.

Shawn

 

[ICON]

When I had the front bumper for a a fresh coat of paint it was a nightmare to try and get the rusted bolts and nuts off, the garage took one whole day to do this - they have all been replaced with the proper galvanized hardware.

 

[Rolf68]

That's right. A pity they didn't use stainless screws by default on such a car.

I'll change them too as soon as I get the opportunity to go under the car.

 

[Stefan T]

I have swapped mine screws to Stainless Steel

 

[ThisoldRoadstr]

I have swapped mine screws to Stainless Steel

This is the solution. Had same issue.

 

[hcsharp]

I've replaced most of the plain steel fasteners with SS. The only parts I haven't found a good replacement for are the clip nuts that many of the under-pan screws go into. I've replaced them all with black oxide but they really need to be stainless.

 

[RobertinWC]

Hello all

Just so you know, stainless fasteners on aluminium can still see galvanic corrosion. Stainless is also subject to crevice corrosion, which occurs when the stainless does not get exposed to oxygen, nuts and bolts, where the nut covers the bolt. The way to prevent either of these from occurring is to use a product called Lanocoat, which is lanolin based. It's very commonly used on sailboats and found in marine supply stores.

Hope this helps
Robert

 

[MCroadster]

I have swapped mine screws to Stainless Steel

Stefan T- Do you know what model SS screws you used to replaced on bottom pan?

 

[ShawnA]

Hi McRoadster,

I bought all of my fasteners at McMaster. I also replaced the ones in the wheel wells.
I could not believe how many there were...

316 Stainless Steel Hex head Screw M6 x 1 mm thread, 16 mm Long 93635A210 2 packs of 25 $13.44
316 Stainless Steel Hex head Screw M6 x 1 mm thread, 20 mm Long 93635A212 1 pack of 25 $7.01
316 Stainless Steel Oversized Washer for M6 screw size, 6.4 mm ID, 18mm OD 95211A160 2 packs of 25 $15.48

Good luck,

Shawn

 

[Kerios]

My SC in Gatwick, UK, replace fasteners progressively during every annual service for my Roadster. As far as I can tell, they've now replaced almost all of the floor pan covers and rear fan fasteners with stainless steel bolts, washers and nuts where applicable; the service tech says it makes life easier for them as well as improves life of the vehicle.

I've replaced many of the bolts when I've fitted new wheel liners, and other supplemetry components using either stainless steel bolts or in some cases for simplicity (and where easy to remove) stainless steel rivets. One of the key places for replacing fasteners with uprated or corrision resistant components as been for the brake calipers and rear anti roll bar mounts, that's made life considerably easier when changing out parts.

 

[MCroadster]

Hi McRoadster,

I bought all of my fasteners at McMaster. I also replaced the ones in the wheel wells.
I could not believe how many there were...

316 Stainless Steel Hex head Screw M6 x 1 mm thread, 16 mm Long 93635A210 2 packs of 25 $13.44
316 Stainless Steel Hex head Screw M6 x 1 mm thread, 20 mm Long 93635A212 1 pack of 25 $7.01
316 Stainless Steel Oversized Washer for M6 screw size, 6.4 mm ID, 18mm OD 95211A160 2 packs of 25 $15.48

Good luck,

Shawn

ShawnA- Thank you for the exact part numbers! I have them ordered and on the way. How long did it take you to replace all of them?

 

[MCroadster]

My SC in Gatwick, UK, replace fasteners progressively during every annual service for my Roadster. As far as I can tell, they've now replaced almost all of the floor pan covers and rear fan fasteners with stainless steel bolts, washers and nuts where applicable; the service tech says it makes life easier for them as well as improves life of the vehicle.

I've replaced many of the bolts when I've fitted new wheel liners, and other supplemetry components using either stainless steel bolts or in some cases for simplicity (and where easy to remove) stainless steel rivets. One of the key places for replacing fasteners with uprated or corrision resistant components as been for the brake calipers and rear anti roll bar mounts, that's made life considerably easier when changing out parts.

Kerios- That is a good idea. I'm having it go in for the annual service this week. Maybe I'll ask them to replace them while they have the car on the lift.

 

[ShawnA]

Hi McRoadster,

Glad you have them coming... It was during the winter on the cold garage floor. I had a large electric heater blowing across
me and the work area.
It took a few hours but I only worked an hour or so at a time.
Some recommendations of tooling: You will need or want some sort of electric or air powered wrench especially for the removal.
I did not use jacks or stands, i just reached under the car to "halfway."
An air powered ratchet with a long body and angled drive let me reach under and remove the crusty ones...
I used another electric wrench to remove them from the wheel wells.

When I removed a group of a given length, I would put a similar quantity of the new bolts and washers in a plastic cup
and spray them with WD-40. It helped them into the corroded, threaded holes.

Good luck,

Shawn

 

[hcsharp]

Anybody found a source for SS clip-nuts that many of the bolts screw into? It's the only rusted fastener I haven't been able to find... except in black oxide, which still rusts.

 

[Rolf68]

Hello

on this site I found those screws that seems to have the same specs.

Buy Metric Full Thread Hexagon Bolts - AccuGroup

They are orderable in A2 / A4 / A4-80 stainless steel

Do you think it's worth to get the A4-80 instead the "basic" A2 ones?

Thanks

 

[ShawnA]

Hi Rolf68,

The A2 stainless corresponds to what we call 304 stainless steel.
It is a good grade of stainless steel.
Generally 316 stainless steel is regarded as the ideal choice for corrosion resistance.
I used the 316 stainless in my car and that corresponds to the A4 grades.
The A2 will work but if the price difference is not too great I would recommend the A4-316 stainless steel.
Remember too, that it is not just the price of the fasteners but your time.
If you do the job yourself you will have a substantial amount of time in vested in the project.

Hi Hcsharp,

The last time you mentioned the SS clip nuts I looked and could not find any...
What I did find that looked encouraging were some grades of nylon and other polymers that
would be corrosion resistant.
The problem with them was that they did not have the larger sizes like 6 mm.
We will have to keep looking something has to turn up...

Shawn

 

[Rolf68]

Hi Rolf68,

The A2 stainless corresponds to what we call 304 stainless steel.
It is a good grade of stainless steel.
Generally 316 stainless steel is regarded as the ideal choice for corrosion resistance.
I used the 316 stainless in my car and that corresponds to the A4 grades.
The A2 will work but if the price difference is not too great I would recommend the A4-316 stainless steel.
Remember too, that it is not just the price of the fasteners but your time.
If you do the job yourself you will have a substantial amount of time in vested in the project.

Shawn

Hello Shawn

Ok I think I'll go for the better ones Thanks for the tip

 

[titaniumdave]

According to most corrosion tables, stainless is worse than regular steel for galvanic issues.
galvanic corrosion chart metals - Google Search:

I saw this quite a bit with Honda NSX which was one of the first all aluminum chassis/body cars. This is what I have gone to: Metric Blue coated fasteners
M6x1.00 Metric Coarse, 16mm Length Under 81706798 - MSC